Hypocalcaemia is a disorder frequently met in mammals, in particular ruminants, especially dairy cows, in connection with the females' delivery (parturition) and is then called milk fever or Parturient Paresis. It is caused by a decline of the calcium concentration in the blood plasma prior to, during and/or after delivery, because the onset of lactation, i.e. the beginning milk production in the mammary glands of the udder requires calcium, which is extracted from the extra-cellular fluid pool, in particular the bloodstream. If the removed calcium is not immediately replenished by either intestinal calcium absorption or by bone calcium resorption, the calcium extraction leads to a decline of the plasma calcium concentration. In particular in dairy cows the demand for calcium in the udder is high in connection with calving in order to produce the colostrum. If the calcium extraction for the milk production in the udder of the cow exceeds the actual calcium supply, hypocalcaemia occurs, which, if untreated, in turn leads to decreased ruminal function, displaced abomasums, slow calving, retained placenta, downer cow syndrome, uterine prolapse, metritis, and finally death.
The normal blood plasma calcium level in cattle is about 1.25 mM, at about 1 mM reduced ruminal function occurs, milk fever occurs below about 0.5 mM, and a further decline to 0.4 mM causes death. Milk fever appears shortly prior to, during or relatively soon after calving; 75% of the incidences appear within 24 h after calving.
The prevalence of milk fever for dairy cows after first and second calving is low, i.e. 0-2%, but is high, i.e. 5-8 and 12-14% for third and fourth calving cows, respectively (ref: “Jerseybladet” June 1996). The increasing prevalence relative to the number of calving is probably a consequence of the demand for high milk producing capacity of present-days dairy cows. Consequently, as modern dairy industry requires a constant high milk yield prevention and treatment of milk fever is an economical important issue.
As the progression of milk fever and other hypocalcaemia related conditions and diseases is fast, the administration of calcium for prevention and treatment has to be fast too.
Thus, the hyper acute treatment of milk fever is only practicable by intra venous administration of a calcium solution, which is to be administered by a veterinarian. In less acute incidents and for prevention purposes, oral administration is a more convenient and cost effective way to administer the necessary calcium supply, which can be given by the farmer himself or a skilled farm-worker.